Question

我有一个场景，在这个场景中，我试图确定公司当月有多少新的“付款人”。我使用的代码有效，我可以记录结果并获取公司预期的新付款方数量。但是，该方法返回0，因为最终代码是在Promise完成之前执行的。

我认为问题在于，promise不是链式的，而是嵌套的，我尝试将它们链接在一起，但是它只是给出了错误。下面的代码明显有什么问题吗？

Parse.Cloud.define('cloudMethod', function(request, response) {
  if (!request.user) {
    response.error('Invalid User')
    return
  }

  // Set up now date
  const now = new Date()
  const thisMonthYear = now.getMonth().toString() + now.getFullYear().toString()

  // Setup empty array to hold new monthly payer matches
  const newMonthlyDonors = []

  // Setup User query
  const User = Parse.Object.extend('User')
  const userQuery = new Parse.Query(User)

  // Step 1: Get company pointer from user
  userQuery
    .equalTo('username', request.user.get('username'))
    .first()
    .then(function(user) {

      // Step 2: Count payers for that company
      var Payment = Parse.Object.extend('Payment')
      var paymentQuery = new Parse.Query(Payment)
      paymentQuery.equalTo('company', user.get('company'))

      // Create a trivial resolved promise as a base case.
      var promise = Parse.Promise.as()

      paymentQuery.distinct('user').then(function(results) {
        // Step 3: Loop through each distinct payer
        _.each(results, function(result) {
          // For each item, extend the promise with a function.
          promise = promise.then(function() {
            // Setup new Payment query
            const firstPaymentQuery = new Parse.Query(Payment)

            /*
              Step 4:
              Query Payment class by this user,
              set payment dates in ascending order
              and then take the first one.
            */
            firstPaymentQuery
              .equalTo('user', result)
              .ascending('paymentDate')
              .first()
              .then(function(firstPayment) {
                // Set up user date
                const firstPaymentDate = new Date(firstPayment.get('paymentDate'))
                const firstPaymentMonthYear = firstPaymentDate.getMonth().toString() + firstPaymentDate.getFullYear().toString()

                /*
                Step 5:
                See if the user's first payment date is equal to the current month
                */
                if (firstPaymentMonthYear === thisMonthYear) {
                  return newMonthlyDonors.push(result)
                }
                else {
                  return
                }
              }, function(error) {
                response.error('Query to get users first payment date failed')
              })
          })
        })

        return promise
      }).then(function() {
        /*
          FIXME:
          This is getting called before the queries above can run.
          Which is why it's returning 0...
        */

        // Return the matches for this month
        response.success(newMonthlyDonors.length)
      }, function(error) {
        response.error('total user count for company failed')
      })
  },
  function(error) {
    console.log('Error retrieving User')
    console.log(error)
  })
})

Answer 1

我会考虑创建一个包含所有诺言const promises = [];的数组，因此，每次有诺言时，都将其推入数组。

然后，您将返回所有这样的承诺：return Promise.all(promises);

Parse.Cloud.define('cloudMethod', function(request, response) {

    ...

    const promises = [];

    promises.push(firstPaymentQuery
          .equalTo('user', result)
          .ascending('paymentDate')
          .first()
          .then(function(firstPayment) { ...

    );

    ...

    // callback if all promises have finished
    Promise.all(promises).then(() => {
        // success
    });

});

这是我通常要做的。

Answer 2

问题是我不是因为import os working_directory = os.path.dirname(__file__) properties_file = os.path.join(working_directory, 'module', 'properties.yaml')中调用的第一个promise的结果而返回查询，所以从未返回该查询中的返回结果。

引用问题中的大部分代码：

此：

_.each()

需要这样：

/*
  Step 4:
  Query Payment class by this user,
  set payment dates in ascending order
  and then take the first one.
*/
firstPaymentQuery…

在兑现承诺之前完成ParseServer云代码功能

2 个答案: